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Cordula Steinkogler

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

The Austrian Outer Space Act, which entered into force in December 2011; and the Austrian Outer Space Regulation, which has been in force since February 2015, form the legal framework for Austrian national space activities. The elaboration of national space legislation became necessary to ensure compliance with Austria’s obligations as State Party to the five United Nations Space Treaties when the first two Austrian satellites were launched in 2012 and Austria became a launching state on its own. The legislation comprehensively regulates legal aspects related to space activities, such as authorization, supervision, and termination of space activities; registration and transfer of space objects; recourse of the government against the operator; as well as implementation of the law and sanctions for its infringement. One of the main purposes of the law is to ensure the authorization of national space activities. The Outer Space Act sets forth the main conditions for authorization, which inter alia refer to the expertise of the operator; requirements for orbital positions and frequency assignments; space debris mitigation, insurance requirements, and the safeguard of public order; public health; national security as well as Austrian foreign policy interests; and international law obligations. The Austrian Outer Space Regulation complements these provisions by specifying the documents the operator must submit as evidence of the fulfillment of the authorization conditions, which include the results of safety tests, emergency plans, and information on the collection and use of Earth observation data. Particular importance is attached to the mitigation of space debris. Operators are required to take measures in accordance with international space debris mitigation guidelines for the avoidance of operational debris, the prevention of on-orbit break-ups and collisions, and the removal of space objects from Earth orbit after the end of the mission. Another specificity of the Austrian space legislation is the possibility of an exemption from the insurance requirement or a reduction of the insurance sum, if the space activity is in the public interest. This allows support to space activities that serve science, research, and education. Moreover, the law also provides for the establishment of a national registry for objects launched into outer space by the competent Austrian Ministry. The first two Austrian satellites have been entered into this registry after their launch in 2012. The third Austrian satellite, launched in June 2017, will be the first satellite authorized under the Austrian space legislation.

Mikhail Zolotov

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.

Chemical and phase compositions of Venus’s surface could reflect history of gas- and fluid-rock interactions, recent and past climate changes, and a loss of water from the Earth’s sister planet. The concept of chemical weathering on Venus through gas-solid type reactions has been established in 1960s after the discovery of hot and dense CO2-rich atmosphere inferred from Earth-based and Mariner 2 radio emission data. Initial works suggested carbonation, hydration, and oxidation of exposed igneous rocks and a control (buffering) of atmospheric gases by solid-gas type chemical equilibria in the near-surface lithosphere. Calcite, quartz, wollastonite, amphiboles, and Fe oxides were considered likely secondary minerals. Since the late 1970s, measurements of trace gases in the sub-cloud atmosphere by Pioneer Venus and Venera entry probes and Earth-based infrared spectroscopy doubted the likelihood of hydration and carbonation. The H2O gas content appeared to be low to allow a stable existence of hydrated and a majority of OH-bearing minerals. The concentration of SO2 was too high to allow the stability of calcite and Ca-rich silicates with respect to sulfatization to CaSO4. In 1980s, the supposed ongoing consumption of atmospheric SO2 to sulfates gained support by the detection of an elevated bulk S content at Venera and Vega landing sites. The induced composition of the near-surface atmosphere implied oxidation of ferrous minerals to magnetite and hematite, consistent with the infrared reflectance of surface materials. The likelihood of sulfatization and oxidation has been illustrated in modeling experiments at simulated Venus conditions.

Venus’s surface morphology suggests that hot surface rocks and fines of mainly mafic composition contacted atmospheric gases during several hundreds of millions years since a global volcanic resurfacing. Some exposed materials could have reacted at higher and lower temperatures in a presence of diverse gases at different altitudinal, volcanic, impact, and atmospheric settings. On highly deformed tessera terrains, more ancient rocks of unknown composition could reflect interactions with putative water-rich atmospheres and even aqueous solutions. Salt-, Fe oxide, or silica-rich formations would indicate past aqueous processes. The apparent diversity of affected solids, surface temperatures, pressures, and gas/fluid compositions throughout Venus’s history implies multiple signs of chemical alteration, which remain to be investigated. The current understanding of chemical weathering is limited by the uncertain composition of the deep atmosphere, by the lack of direct data on the phase composition of surface materials, and by the uncertain data on thermodynamics of minerals and their solid solutions. In the preparation for further entry probe and lander missions, rock alteration needs to be investigated through chemical kinetic experiments and calculations of solid-gas(fluid) equilibria to constrain past and present processes.

Anni Määttänen and Franck Montmessin

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.

Although resembling an extremely dry desert, planet Mars hosts clouds in its atmosphere. Every day somewhere on the planet a part of the tiny amount of water vapor held by the atmosphere can condense as ice crystals to form cirrus-type clouds. The existence of water ice clouds has been known for a long time, and they have been studied for decades, leading to the establishment of a well-known climatology and understanding of their formation and properties. Despite their thinness, they have a clear impact on the atmospheric temperatures, thus affecting the Martian climate.

Another, more exotic type of clouds forms as well on Mars. The atmospheric temperatures can plunge to such frigid values that the major gaseous component of the atmosphere, CO2, condenses as ice crystals. These clouds form in the cold polar night where they also contribute to the formation of the CO2 ice polar cap, and also in the mesosphere at very high altitudes, near the edge of space, analogously to the noctilucent clouds on Earth. The mesospheric clouds are a fairly recent discovery and have put our understanding of the Martian atmosphere to a test.

On Mars, cloud crystals form on ice nuclei, mostly provided by the omnipresent dust. Thus, the clouds link the three major climatic cycles: those of the two major volatiles, H2O and CO2; and that of dust, which is a major climatic agent itself.

John C. Bridges

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

Mars, which has a tenth of the mass of Earth, has cooled as a single lithospheric plate. Current topography gravity maps and magnetic maps do not show signs of the plate tectonics processes that have shaped the Earth’s surface. Instead, Mars has been shaped by the effects of meteorite bombardment, igneous activity, and sedimentary—including aqueous—processes. Mars also contains enormous igneous centers—Tharsis and Elysium, with other shield volcanoes in the ancient highlands. In fact, the planet has been volcanically active for nearly all of its 4.5 Gyr history, and crater counts in the Northern Lowlands suggest that may have extended to within the last tens of millions of years. Our knowledge of the composition of the igneous rocks on Mars is informed by over 100 Martian meteorites and the results from landers and orbiters. These show dominantly tholeiitic basaltic compositions derived by melting of a relatively K, Fe-rich mantle compared to that of the Earth. However, recent meteorite and lander results reveal considerable diversity, including more silica-rich and alkaline igneous activity. These show the importance of a range of processes including crystal fractionation, partial melting, and possibly mantle metasomatism and crustal contamination of magmas. The figures and plots of compositional data from meteorites and landers show the range of compositions with comparisons to other planetary basalts (Earth, Moon, Venus). A notable feature of Martian igneous rocks is the apparent absence of amphibole. This is one of the clues that the Martian mantle had a very low water content when compared to that of Earth.

The Martian crust, however, has undergone hydrothermal alteration, with impact as an important heat source. This is shown by SNC analyses of secondary minerals and Near Infra-Red analyses from orbit. The associated water may be endogenous.

Our view of the Martian crust has changed since Viking landers touched down on the planet in 1976: from one almost entirely dominated by basaltic flows to one where much of the ancient highlands, particularly in ancient craters, is covered by km deep sedimentary deposits that record changing environmental conditions from ancient to recent Mars. The composition of these sediments—including, notably, the MSL Curiosity Rover results—reveal an ancient Mars where physical weathering of basaltic and fractionated igneous source material has dominated over extensive chemical weathering.

Dmitry V. Bisikalo, Pavel V. Kaygorodov, and Valery I. Shematovich

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

The discovery of exoplanets is an outstanding achievement of observational astronomy. A significant portion of known exoplanets are the hot Jupiter—planets, having no analogue in the Solar system. These are giant planets, having a mass on the order of the mass of Jupiter, and orbiting very close to their host stars. The discovery of these objects raises a number of fundamental questions—how they are formed, what their evolution is, which properties their atmospheres have, etc. Due to relatively easy detection and observation, hot Jupiters provide a large amount of observational data and can be studied in detail using modern astronomical instruments.

The atmospheres of hot Jupiters must differ significantly from the ones of giant planets in the Solar system that we knew before. The proximity of these objects to the host stars causes the strong gravitational influence, significant stellar irradiation, and close interaction of their atmospheres with stellar plasma. The observations support this assertion—light curves, obtained in the near ultraviolet wavelength range for transiting hot Jupiters, demonstrate evidence of large gaseous envelopes around these planets. To explain the observed features, we need to find answers to a many questions regarding the stability of hot Jupiter atmospheres, their dynamics, heating and cooling mechanisms, etc. A large amount of work has been performed by many scientific groups in the world to get the answers, but we are still at the beginning of the long road to understanding the processes taking place in the atmospheres of hot Jupiters. The reviews on the observational data currently available on the atmospheres of hot Jupiters and the modern theoretical models developed for their explanation will be presented.

Valery I. Shematovich and Dmitry V. Bisikalo

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

The uppermost layers of a planetary atmosphere, where the density of neutral particles is vanishingly low, are commonly called the exosphere or the planetary corona. Since the atmosphere is not completely bound to the planet by the planetary gravitational field, light atoms, such as hydrogen and helium with sufficiently large velocities, can escape from the upper atmosphere into interplanetary space. This process is commonly called Jeans escape, and it depends on the temperature of the ambient atmospheric gas at an altitude where the atmospheric gas is virtually collisionless. The heavier carbon, nitrogen, and oxygen atoms can escape from the atmospheres of the terrestrial planets only through non-thermal processes such as photo- and electron-impact dissociation, charge exchange, atmospheric sputtering, and ion pick-up. Theories of planetary exospheres have been based on ground-based and space observations of emission features such as the 121.6 nm Ly-α and 102.6 nm Ly-β hydrogen lines, the 58.4 nm helium line, and the 130.4 and 135.6 nm atomic oxygen lines. Such observations, together with in situ mass-spectrometer measurements, as at Titan, allow the density and temperature height profiles of the exospheric components to be constructed. The measurements reveal that planetary coronas contain both a fraction of thermal neutral particles with a mean kinetic energy corresponding to the exospheric temperature and a fraction of hot neutral particles with mean kinetic energy much higher than the exospheric temperature. These suprathermal (hot) atoms and molecules are a direct manifestation of the non-thermal processes taking place in the atmospheres. These hot particles lead to the atmospheric escape, determine the coronal structure, produce non-thermal emissions, and react with the ambient atmospheric gas triggering hot atom chemistry.

One of the brightest manifestations of these processes is a formation of hot oxygen corona around terrestrial planets. Oxygen atom is one of the lightest among heavy atmospheric species, so it is a best species to form corona, and another important aspect is that it produces a lot of observational evidence. The transport of suprathermal oxygen atoms to exospheric heights leads to the formation of hot oxygen coronas around Venus, Earth, and Mars. It has been well established by both observations and theoretical calculations that hot oxygen is an important constituent in the transition region between upper thermosphere and exosphere at terrestrial planets.

The study of the planetary coronas is based on direct observations and numerical simulations. It is a rarefied gas, ttherefore, production and transport of suprathermal particles into the corona requires solving a Boltzmann equation or a DSMC simulation. The stochastic simulation method had been widely used to investigate the formation, kinetics, and transport of suprathermal particles in the hot planetary coronas. This approach was first used to study the formation of the hot oxygen geocorona, taking into account the exothermic chemistry and the precipitation of magnetospheric protons and high-energy O+ ions from the ring current. It was found that only atmospheric sputtering results in the formation of the escape flux of energetic oxygen atoms, providing an important source of heavy atoms for the magnetosphere and geospace. A stochastic modeling approach was also applied to study the escape of hot oxygen atoms from the upper atmosphere of Mars and Venus; the kinetics and transport of suprathermal atoms and molecules in the hot oxygen corona at Jovian satellite Europa, which is an example of a highly non-equilibrium near-surface atmosphere; and the hot extended corona at Saturnian satellite Titan, which was directly measured by the spacecraft Cassini.

Wendell Mendell

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

Emergence of ballistic missile technology after the Second World War enabled human flight into Earth’s orbit, fueling the imagination of those fascinated with science, technology, exploration, and adventure. The performance of astronauts in the early flights assuaged concerns about the functioning of “the human system” in the absence of normal gravity. However, researchers in space medicine have observed degradation of crews after longer exposure to the space environment and have developed countermeasures for most of them, although significant challenges remain. With the dawn of the 21st century, well-financed and technically competent commercial entities began to provide more affordable alternatives to historically expensive and risk-averse government-funded programs. Space’s growing accessibility has encouraged entrepreneurs to pursue plans for potentially autarkic communities beyond Earth, exploiting natural resources on other worlds. Should such dreams prove to be technically and economically feasible, a new era will open for humanity with concomitant societal issues of a revolutionary nature.

Frans von der Dunk

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

International space law is generally considered to be a branch of public international law. In that sense, it constitutes a “subset of rules, rights and obligations of states within the latter specifically related to outer space and activities in or with respect to that realm.” Dealing with an inherently international realm, much of it had been developed in the context of the United Nations, where the key treaties are even adhered to by all major space-faring countries. In addition, other sources—including not only customary international law but also such disputed concepts as “soft law” and political guidelines and recommendations—also contributed to the development of a general framework legal regime for all of mankind’s endeavors in or with respect to outer space.

Originally, this predominantly included scientific and military/security-related activities, but with the ongoing development of technology and a more practical orientation, it increasingly came to encompass many more civilian and, ultimately, even commercial activities, largely through downstream applications originating from or depending on space technology and space activities.

Important here are the overarching, usually more theoretical aspects of international space law, which include how it was developed or continues to be developed, what special roles do “soft law” or the military aspects of space activities play in this regard, and how do national space laws (also) serve as a tool for interpretation of international space law.

Also important is the special category of launches and other space operations in the sense of moving space objects safely into, through and—if applicable—back from outer space. Without such operations, space activities would be impossible, yet they bring with them special concerns; for instance, in terms of liability, the creation of space debris and even the legal status and possible commercialization of natural resources produced from celestial bodies.

Finally there are the major categories of space applications—as these have started to impact everyday life on earth: the involvement of satellites in communications infrastructures and services, the most commercialized area of space applications yet; the special issue of space serving to mitigate disasters and their consequences on earth; the use of satellites for remote sensing purposes ranging from weather and climate monitoring to spying; and the use of satellites for positioning, navigation, and timing.

Peter Stubbe

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

Space debris has grown to be a significant problem for outer space activities. The remnants of human activities in space are very diverse; they can be tiny paint flakes, all sorts of fragments, or entirely intact—but otherwise nonfunctional spacecraft and rocket bodies. The amount of debris is increasing at a growing pace, thus raising the risk of collision with operational satellites. Due to the relative high velocities involved in on-orbit collisions, their consequences are severe; collisions lead to significant damage or the complete destruction of the affected spacecraft. Protective measures and collision avoidance have thus become a major concern for spacecraft operators. The pollution of space with debris must, however, not only be seen as an unfavorable circumstance that accompanies space activities and increases the costs and complexity of outer space activities. Beyond this rather technical perspective, the presence of man-made, nonfunctional objects in space represents a global environmental concern. Similar to the patterns of other environmental problems on Earth, debris generation appears to have surpassed the absorption capacity of the space environment. Studies indicate that the evolution of the space object environment has crossed the tipping point to a runaway situation in which an increasing number of collisions―mostly among debris―leads to an uncontrolled population growth. It is thus in the interest of all mankind to address the debris problem in order to preserve the space environment for future generations.

International space law protects the space environment. Article IX of the Outer Space Treaty obligates States to avoid the harmful contamination of outer space. The provision corresponds to the obligation to protect the environment in areas beyond national jurisdiction under the customary “no harm” rule of general environmental law. These norms are applicable to space debris and establish the duty not to pollute outer space by limiting the generation of debris. They become all the more effective when the principles of sustainable development are taken into account, which infuse considerations of intra- as well as inter-generational justice into international law. In view of the growing debris pollution and its related detrimental effects, it is obvious that questions of liability and responsibility will become increasingly relevant. The Liability Convention offers a remedy for victims having suffered damage caused by space debris. The launching State liability that it establishes is even absolute for damage occurring on the surface of the Earth. The secondary rules of international responsibility law go beyond mere compensation: States can also be held accountable for the environmental pollution event itself, entailing a number of consequential obligations, among them―under certain circumstances―a duty to active debris removal. While international law is, therefore, generally effective in addressing the debris problem, growing use and growing risks necessitate the establishment of a comprehensive traffic management regime for outer space. It would strengthen the rule of law in outer space and ensure the sustainability of space utilization.

Kun Wang and Randy Korotev

This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.

For thousands of years, people living in Egypt, China, Greece, Rome, and other parts of the world have been fascinated by shooting stars, which are the light and sound phenomena associated with meteorite impacts. The earliest written record of meteorite fall is logged by Chinese chroniclers back to 687 bce. However, centuries before that, Egyptians have been using “heavenly iron” to make their first iron tools, including a dagger recently found in King Tutankhamun’s tomb that dates back to the 14th century bce. Even though human beings have a long history of observing meteors and utilizing meteorites, we did not start to recognize their true celestial origin until the Age of Enlightenment. In 1794 German physicist and musician Ernst Chladni was the first to summarize the scientific evidences and to demonstrate that these unique objects are indeed from outside of the Earth. After more than two centuries of joint efforts by countless keen amateur, academic, institutional, and commercial collectors, more than 55,000 meteorites have been catalogued and classified in the Meteoritical Bulletin Database. This number is continually growing, and meteorites are found all over the world, especially in dry and sparsely populated regions such as Antarctica and Sahara Desert. Although there are thousands of individual meteorites, they can be handily classified into three broad groups by simple examinations of the specimens. The most common type is stony meteorite, which is made of mostly silicate rocks. Iron meteorites are the easiest to be preserved for thousands (or even millions) of years on the Earth’s surface environments, and they are composed of more than 90% iron and nickel metals. The stony-irons contain roughly the same amount of metals and silicates, and these spectacular meteorites are the favorites of many collectors and museums.

After 200 years, meteoritics (the science of meteorites) has grown out of its infancy and become a vibrant area of research today. The general directions of meteoritic studies are: (1) mineralogy, identifying new minerals or mineral phases that rarely or seldom found on the Earth; (2) petrology, studying the igneous and aqueous textures that given meteorites’ unique appearances and providing information about geologic processes on the bodies upon which the meteorites originates; (3) geochemistry, characterizing their major, trace elemental and isotopic compositions and conducting interplanetary comparisons; and (4) chronology, dating the ages of the initial crystallization and later on impacting disturbances. Meteorites are the only extraterrestrial samples other than Apollo lunar rocks that we can directly analyze in laboratories. Through the studies of meteorites, we have quested a vast amount of knowledge about the origin of the Solar System, the nature of the molecular cloud, the solar nebula, the nascent Sun and its planetary bodies including the Earth, Mars, Moon, and many asteroids. In fact, the 4.6-billion-year age of the whole Solar System is solely defined by the oldest age dated in meteorites, which marked the beginning of everything we appreciate today.